The present invention relates generally to circuit breakers. More specifically, the present invention relates to an auxiliary switch for a circuit breaker which is capable of switching substantially the rated interrupt current of the circuit breaker.
Control panel systems, having a variety of panel mounted circuit breakers mounted thereon, are often sold in both the United States and Europe to provide branch circuit protection or supplementary (equipment) protection. By way of example, circuit breakers are often mounted in theater lighting control panel systems to provide protection for branch circuits which supply electrical power to the various lights of a theater. Alternatively, circuit breakers can also be mounted in control panels to provide dedicated supplementary protection to equipment such as computers, power supplies or copying machines.
Circuit protection standards vary between the United States and Europe, and impose different performance requirements on the circuit breakers involved. For example, U.S. standards rarely allow the provision of a disconnect to the neutral (return) side of a circuit load, while European standards often require it. European standards for a neutral disconnect effectively requires the addition of another switch, capable of handling the rated interrupt current capacity of the circuit breaker, when connected in series with the circuit breaker and the load. Rated interrupt current, i.e., interrupting rating, is defined in article 100 of the 1996 edition of the National Electric Code, published by the National Fire Protection Association, Quincy, Mass., as: xe2x80x9cthe highest current at rated voltage that a device is intended to interrupt under standard test conditionsxe2x80x9d. The interrupt current and the standard test conditions for a device, such as a circuit breaker, would typically be specified in an industry excepted standard, e.g., UL 1077, titled Standard For Supplementary Protectors For Use In Electrical Equipment, or UL489, titled Standard For Molded Case Circuit Breakers And Circuit Breaker Enclosures. Prior art attempts to modify existing U.S. circuit breakers to provide neutral side disconnects involved stacking a second pole up against the single pole circuit breaker, effectively doubling the width and size of such an assembly.
However, space is a premium in control panel systems. In the telecommunication industry, for example, telecommunication equipment designers can earn bonuses of up to $1000 for every square inch of panel space saved. Consequently, there is often very little panel space to accommodate the additional second pole for the circuit breakers without an expensive redesign of the system. This is especially critical when the additional requirements increase the overall package width, since the circuit breakers are often stacked side by side, leaving very little space in between for growth.
Auxiliary switches are often mounted to the bottom portions of circuit breakers to provide an extra set of switching contacts without a significant increase in overall package size or width. However, auxiliary switches are primarily used to indicate status of the circuit breaker, e.g., whether the circuit breaker is open or closed, and typically have current switching capacities which are much lower than the interrupt current capacity rating of the main breaker. The low power auxiliary switches are constructed of much smaller components and require much less space to actuate than the main contacts of the circuit breaker.
To construct an auxiliary switch capable of switching the rated interrupt current capacity of its associated circuit breaker with a minimum impact in overall package width is problematic for several reasons. For example, the contact gap spaces and spring forces for the auxiliary switch must increase, tending to increase the package size and width. Also, since the auxiliary contacts are mechanically actuated by the main breaker contacts, the increased spring forces from the auxiliary switch actuator acting on the main breaker contacts may significantly change the main breaker contact pressure. This can result in excessive arcing and premature circuit breaker contact wear.
Another significant factor which tends to make the auxiliary switch package grow is that the higher power requirements can result in greater arcing during make (make contact) or break (break contact) of the auxiliary contacts. This increases the possibility of welding the contacts together or leaving debris and carbon deposits on the contacts. This problem is often minimized in the main circuit breaker with a lateral wiping action designed between the movable and stationary contacts of the main breaker. The wiping action is used to clean the contacts and shear away any welds as the contacts make or break. That is, the moveable contacts of the main circuit breaker pivots on a moveable contact lever to make contact with the stationary contact. A generally kidney shaped slot at the pivot point of the movable contact lever is fundamental to this arcuate motion. This slot is easily elongated to provide for over travel in the lateral directions of the contacts relative to each other, which results in the wiping action.
However, auxiliary switch contacts are typically designed to have a substantially linear motion when bridging the contact gaps (bridge contacts), rather than the arcuate motion described above for the main breaker contacts. Problematically, the bridge contacts are not conducive to providing a wiping action in the lateral direction. The arcing problem can be compensated for by increasing the size of the auxiliary contacts and their associated contact gaps, but this tends to unduly increase the overall package size and width.
Accordingly, there is a need for an improved auxiliary switch for a circuit breaker, which is capable of switching the rated interrupt current capacity of the associated circuit breaker.
The present invention offers advantages and alternative over the prior art by providing an auxiliary switch for a circuit breaker capable of switching the rated interrupt current capacity of the breaker. The auxiliary switch/circuit breaker assembly can be used to provide neutral disconnects to an existing control panel system to meet European standards.
These and other advantages are accomplished in an exemplary embodiment of the invention by providing a circuit breaker assembly comprising a circuit breaker and an auxiliary switch. The circuit breaker has a predetermined rated interrupt current capacity, and includes a movable contact lever having a circuit breaker moveable contact disposed thereon. The contact lever has an open position and a closed position. The auxiliary switch includes a switch housing mounted in an opening defined by the circuit breaker. An auxiliary actuator is movably mounted within the switch housing and has an upper portion of the auxiliary actuator protruding into the opening of the circuit breaker from the switch housing. An auxiliary moveable contact member has an auxiliary moveable contact disposed thereon, the member is moveably mounted to the auxiliary actuator. A contact spring acts between the auxiliary actuator and the auxiliary moveable contact member. An auxiliary stationary contact is arranged in the switch housing for engagement with the auxiliary moveable contact. A return spring is disposed between the switch housing and auxiliary actuator urging the auxiliary stationary and moveable contacts apart. The auxiliary switch is adapted to switch substantially the rated interrupt current of the circuit breaker through the moveable and stationary auxiliary contacts when the moveable contact lever of the circuit breaker moves from the open position to the close position, thereby depressing the auxiliary actuator to have the auxiliary moveable contact make contact with the auxiliary stationary contact.
In an alternative embodiment of the invention the overall width of the auxiliary switch is substantially equal to or less than the overall width of the circuit breaker.
Several embodiments of the auxiliary switch disclose various features which contribute to increasing the interrupt current rating and/or down sizing the width of the auxiliary switch. Among them are:
an early make, late break of the auxiliary contacts compared to the circuit breaker contacts;
an inertia dampening fly wheel attached to the actuator of the switch to enhance the early make/late break feature;
a wiping action between the moveable and stationary contacts of the auxiliary switch to clean off welding and debris deposited from arcing;
dual auxiliary contacts to enhance the contact area with little impact on package size and width; and
a positioning of the auxiliary actuator on the contact lever of the circuit breaker to prevent the spring forces acting on the actuator from affecting circuit breaker contact pressure.